Dd is 8 months old and loves to put her mouth (and sometimes most of her face it seems)in the water and drink it. She does it in the tub too. Silly girl! Anyway, I don't worry about it too much because I know she is not drinking alot of water.
I empty the pool out every evening, mostly because of the mosquitos. Then I lean it against something so it can air dry. I haven't needed to "wash" it yet. I rinse it out every morning before putting water in it for the day. I guess when I do wash it, I'll use some dish soap or something.
She wears a swim diaper.